This invention relates to a fuel system for use in delivering fuel under high pressure to a cylinder of an associated compression ignition internal combustion engine, and to a fuel pump suitable for use in such a system.
In order to ensure that the level of emissions produced by an engine falls within acceptable levels, it is desirable to be able to control the fuel pressure at which fuel is injected to a cylinder of an engine independently of the timing of fuel delivery. Where the fuel system includes injectors with integral fuel pumps, this has been achieved by using separate valves to control the injection pressure and the timing of injection. The valve controlling injection pressure is typically mounted upon the side of the injector housing with the result that the dimensions of the injector are relatively large thus the injector may not be suitable for use in some applications. Further, the location of the valve results in a relatively large dead volume which reduces responsiveness and the passages connecting the valve to the remainder of the injector are relatively difficult to produce.
According to the present invention there is provided a fuel system comprising a fuel pump arranged to deliver fuel to a single fuel injector, the fuel pump being operable to control the timing of commencement of fuel pressurization, the injector being controllable to control the timing of fuel injection, the fuel pump and injector being spaced apart from one another, a high pressure fuel line interconnecting the fuel pump and the injector, and a controller controlling the operation of the fuel pump and the injector.
The controller is conveniently arranged to control operation of the fuel pump to commence pressurization at an instant a predetermined time interval in advance of the time at which injection is to commence. The commencement of pressurization is conveniently achieved by closing a control valve. The control valve may include a valve member which extends and is moveable along an axis generally parallel to or generally coaxial with the pumping plunger of the fuel pump.
In an alternative arrangement, the controller may control the injection pressure by controlling the quantity of fuel supplied to the fuel pump. In a further alternative, the fuel pump may include a spill valve controlling the termination of injection.
The invention further relates to a fuel pump comprising a plunger reciprocable within a bore to deliver fuel to an outlet connector, and a control valve controlling the timing of pressurization of fuel by the pump, the control valve comprising a valve member slidable within a bore which extends in a direction generally parallel to an axis of the bore within which the plunger is reciprocable. The bores are conveniently generally coaxial.
By locating the control valve generally coaxially within the pump, manufacture of the pump can be simplified, and the dead volume within the pump can be reduced. Further, the pump is relatively compact compared to an arrangement in which the axis of the bore of the valve extends perpendicularly to the axis of the plunger bore, thus simplifying installation and increasing the range of applications in which the pump can be used.